The cosignatories of the COGENconsensus statement attempt to refute our remarks and concerns about the increased use of preimplantation genetic screening (PGS) by presenting the same low-level 'evidence' they continuously use to advocate the widespread adoption of PGS (BioNews 840). In an attempt to once more explain our concerns, there are three serious issues that we will address again.

First, there is no high-level evidence available that demonstrates that PGS will increase the chance for subfertile couples to achieve a live birth. The few trials that have been conducted suffer from serious design, analysis and interpretation issues (1). Yes, randomised controlled trials (RCTs) have been performed, but a randomised trial of low quality is still a low level of evidence despite the fact that patients were randomised. Also, performing a meta-analysis on these flawed RCTs does not magically result in evidence. Unfortunately, many clinics do not bother to wait for evidence, even though they are aware that evidence is lacking. This is emphasised in a survey published alongside the COGEN consensus statement: while 77 percent of all clinics state that PGS is offered in their clinic, 84 percent of those state that more randomised trials are needed to support the use of PGS.

Second, the presentation of the available data is misleading to patients. PGS is being marketed as a technology that increases IVF success rates, but whose success rates are they talking about? It is clear that the reason for couples to attend a fertility clinic is to obtain a healthy liveborn child. And it is this gold-standard success rate in ART (assisted reproductive technology), namely singleton, term-gestation, live-birth rate per cycle initiated, which can never be increased by PGS, simply because PGS does not cure or restore embryos but is solely used as a selection tool. That is what our title referred to. The pro-PGS advocates refuse to make this clear to their patients and instead focus on alternative 'outcomes' such as miscarriages, multiple pregnancy rates and the birth of children with congenital malformations. And even here, high-level evidence is lacking. Patients should never be misled. If a physician repeated the COGEN cosignatories in their reply to us ('unless you use PGS you are more likely to implant aneuploid embryos and implanting aneuploid embryos severely increases your chance of a miscarriage and reduces your chances of having a baby') to a patient, they would be doing just that. Not using PGS does not reduce your chances of having a baby.

Third, we raise concern about the commercialisation of PGS technology. The authors agree that ties with commercial companies exist among the cosignatories but they state that 'this is not a commercially sponsored statement and many of signatories have no links to PGS companies'. Yet it is evident that those who have a financial interest in the product that is under discussion are more likely to highlight the pros than the cons and will not state something that has the potential to negatively affect the sales of that product. Of course, companies are entitled to promote their products. But we strongly feel that when it comes to 'products' in the field of medicine there is only one reason to use those products and that is proven benefit for the patient. Here the application of evidence-based medicine is the moral obligation of all medical professionals (2).

We do not have the illusion that this discussion will change the minds of those that continue to push use of PGS forward (for whatever motivation); beliefs and interests are hard to overcome. But we do hope it will spur further scientific research, more awareness of the issues we raise and drive regulatory bodies to make evidence-based recommendations on the (ab)use of PGS and other reproductive technologies now and in the future.

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